Animals 2012, 2, 108-126; doi:10.3390/ani2020108
OPEN ACCESS
animals
ISSN 2076-2615
www.mdpi.com/journal/animals
Article
Carbon Footprints for Food of Animal Origin: What are the
Most Preferable Criteria to Measure Animal Yields?
Gerhard Flachowsky 1,* and Josef Kamphues 2
1
2
Institute of Animal Nutrition, Friedrich-Loeffler-Institute (FLI), Federal Research Institute for
Animal Health, Bundesallee 50, 38116 Braunschweig, Germany
Institute of Animal Nutrition, University of Veterinary Medicine Hannover, Foundation,
Bischofsholer Damm 15, 30173 Hannover, Germany; E-Mail: [email protected]
* Author to whom correspondence should be addressed; E-Mail: [email protected];
Tel.: +49-531-514-112; Fax: +49-531-596-3299.
Received: 21 January 2012; in revised form: 5 March 2012 / Accepted: 13 March 2012 /
Published: 27 March 2012
Simple Summary: Greenhouse gas emissions from animal production are substantial
contributors to global emissions. Therefore Carbon Footprints (CF) were introduced to
compare emissions from various foods of animal origin. The CF for food of animal origin
depends on a number of influencing factors such as animal species, type of production,
feeding of animals, level of animal performance, system boundaries and output/endpoints
of production. Milk and egg yields are more clearly defined animal outputs of production
than food from slaughtered animals. Body weight gain, carcass weight gain, meat, edible
fractions of carcass or edible protein are measurable outputs of slaughtered animals. The
pros and contras of various outcomes under special consideration of edible protein are
discussed in this paper.
Abstract: There are increasing efforts to determine the origin of greenhouse gas emissions
caused by human activities (including food consumption) and to identify, apply and exploit
reduction potentials. Low emissions are generally the result of increased efficiency in
resource utilization. Considering climate related factors, the emissions of carbon dioxide,
methane and laughing gas are summarized to so-called carbon footprints (CF). The CF for
food of animal origin such as milk, eggs, meat and fish depend on a number of influencing
factors such as animal species, type of production, feeding of animals, animal performance,
system boundaries and outputs of production. Milk and egg yields are more clearly defined
animal yields or outcomes of production than food from the carcasses of animals. Possible
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endpoints of growing/slaughter animals are body weight gain, carcass weight gain (warm
or cold), meat, edible fractions or edible protein. The production of edible protein of
animal origin may be considered as one of the main objectives of animal husbandry in
many countries. On the other hand, the efficiency of various lines of production and the CF
per product can also be easily compared on the basis of edible protein. The pros and
contras of various outputs of animal production under special consideration of edible
protein are discussed in the paper.
Keywords: food of animal origin; carbon footprints; system boundaries; milk; eggs; carcass;
meat; edible protein
1. Introduction
The current world situation is characterized by a growing population and a higher need for feed and
food. These facts are, in turn, associated with a growing demand for limited natural resources such as
fuel, land area, water, etc., and with elevated emissions with greenhouse gas (GHG) potential. Such
gases can include, e.g., carbon dioxide (CO2), methane (CH4), laughing gas (N2O) and other
substances (e.g., N, P, trace elements, etc.; (e.g., [1–5]). During the last few years special attention has
been devoted to various gases because of their greenhouse gas potential. This increase is discussed in
the context of global warming and possible climate change [2].
Agriculture and especially animal husbandry are considered as important greenhouse gas
sources because of the high greenhouse potential of their emissions (e.g., CO2 × 1; CH4 × 23 and
N2O × 296; [2]). So-called Carbon Footprints (CF; Life cycle assessments (LCA), Eco-Balances)
consider the greenhouse gas potential of climate relevant gases and are expressed relative to one gram
or kilogram of CO2 equivalent (CO2eq) per product unit.
Various authors calculated such CF for agriculture in general, but also for separate segments. For
example, according to Steinfeld et al. [1] livestock production contributes about 18% to the global
anthropogenic GHG emissions. O`Mara [6] has reported that animal agriculture is responsible for
8–10.8% of the global GHG emissions. After Lesschen et al. [7] livestock farming contributes to
global warming with about 10% of total GHG emissions from the EU-27. FAO [4] asserts that the
global dairy sector contributes with 3.0 to 5.1% to total anthropogenic greenhouse gases, but Sevenster
and Jones [8] calculated only 1.2% from dairy livestock to the global greenhouse gas emissions.
The highest variation of global GHG emissions from livestock is mentioned by Herrero et al. [9]
with a range from 8 to 51%. Detailed information about the GHG emission in the EU is given by
Leip et al. [10]. From a total of about 660 million tonnes CO2eq per year from livestock, about 65%
come from ruminants (production of milk, beef, sheep and goats [10]). Methodical and regional
differences make it difficult to compare such values, to make conclusions or to give data based advice
to policy makers. The objectives of CF are to sensitize producers and consumers for an efficient use of
fossil carbon sources and to reduce greenhouse gas emissions per unit of product.
During the last 10 years many studies dealt with calculations of CF for almost all products resulting
from human activities, including production of food of animal origin (e.g., [4,5,7,10–17]). The large
Animals 2012, 2
110
range in CF when comparing results of various authors depends on many influencing factors as
exemplary shown in Tables 1 and 2 for milk and beef. The CF for milk varies between 0.4 and 1.5 kg
CO2eq/kg milk, taking different world regions into account, between 1.3 (Europe and North America)
and 7.5 kg CO2eq/kg in sub-Saharan Africa [4] (see Table 1). Furthermore, most authors considered
only the emissions during the production, but sometimes processing, transport and trade are also
included in the calculation.
Table 1. Examples of Carbon Footprints (CF) (kg CO2eq/kg milk) depending on the type
of production.
Type of production/farming
Country
Conventional
Organic
Germany
0.83
0.84
Germany
0.85
0.78
Sweden
0.90
0.94
Germany
0.94
0.88
The NL
0.97
1.13
Germany
0.98
0.92
Sweden
0.99
0.94
UK
1.06
1.23
Austria
1.20
1.00
UK
1.20
1.30
Germany
1.30
1.30
The NL
1.40
1.50
UK
1.6 (1.0–3.2)
1.3 (0.9–2.4)
Without differentiation in conventional/organic
Germany
0.40 (40 kg milk/day)
0.55 (20 kg milk/day)
(model calculation)
1.00 (10 kg milk/day)
Germany
0.65
New Zealand
0.65–0.75
0.8–1.4 (on farm)
Literature review
0.9–1.8 (on farm + post farm emissions)
New Zealand
0.86
Germany
0.98 (10,000)–1.35 (6,000 kg milk/year; see Table 3)
Sweden
1.00
Canada
1.00
UK
1.06
USA
1.09
EU-27
1.3 (1.0–2.3)
Ireland
1.3–1.5
Global
2.4 (1.3–7.5)
References
[18]
[14]
[19]
[13]
[20]
[21]
[22]
[12]
[23]
[24]
[25]
[26]
[27]
[28]
[28]
[28]
[29]
[30]
[8]
[31]
[32]
[33]
[34]
[12]
[35]
[7]
[36]
[4]
Still higher variations of CF are described for beef (see Table 2). The values are influenced by body
weight gain, feeding, production system and system limits. There are many ways for CF calculation of
the yield of growing animals such as body weight gain, hot standard carcass weight, empty body weight,
Animals 2012, 2
111
meat, meat plus edible organs or edible protein. In dependence on the calculation basis, the authors
found a high variation in CF for beef. The highest values are given for beef cows (Table 2). In general all
the results indicate (e.g., [6,37,38]) that activities which are targeted at improvements in productivity
and efficiency of resource use will result in a lower GHG emission or lower CF per unit of product.
Table 2. Examples for CF (kg CO2eq/kg carcass weight gain) of beef cattle depending on
type of production.
Type of production/farming
Country
Conventional
Organic
Germany
8.5
29.0 (beef cow)
Germany
8.7/10.1
10.2
Australia
9.9(grain finished)
12.0(grass finished)
10
32–40
Global
(intensive–dairy beef)
(organic–suckler beef)
Germany
13.3
11.4
Germany
15.2
17.5
UK
15.8
18.2
Ireland
23.6
20.2
Global
24.5
20.9
Without differentiation in conventional/organic
Germany
5.6 (6,000)–14.6 (10,000 kg milk per cow per year, see Table 3)
Canada
5.9–10.4
Germany
7.0–23.0
8.4 (fattening of calves from dairy cows)
Germany
16.8 (fattening of calves from beef cows)
Sweden
10.1
Ireland
13.0 (11.3–15.6)
15.6 (fattening of calves from dairy cows)
Global
20.2 (fattening of calves from beef cows)
16.9–19.9 (fattening of calves from dairy cows)
EU
27.3 (fattening of calves from beef cows)
Japan
19.6
Japan
36.4 (beef cows, fattening bulls; 40% meat yield)
References
[39]
[18]
[37]
[24]
[13]
[40]
[12]
[41]
[42]
[32]
[34]
[28]
[14]
[43]
[41,44]
[4]
[45]
[46]
[47]
Apart from the factors mentioned above, the allocation of animal products (e.g., [15,26,32,43,48])
may be used whenever systems under study generate more than one saleable output (e.g., milk and
meat) or various co-products. Such studies also influence the results of LCA (e.g., [32,37,48]).
Mass-based and economic-based allocations were applied. For example Zehetmeier et al. [32,38]
calculated CF of 1.35 and 0.98 kg CO2eq per kg milk of cows producing 6,000 and 10,000 kg milk per
year, respectively. In the case of lower milk yield, beef was produced by calves of dairy cows with a
CF of 5.58 kg; in the case of higher milk yields, beef cows are needed to produce sufficient beef and
the CF increased to 14.62 kg CO2eq per kg beef. Under consideration of economic aspects (prices for
milk and beef; economic allocation), the CF for milk decreased, those of beef increased.
Animals 2012, 2
112
Under consideration of all aspects mentioned above, it is extremely difficult to compare results of
LCA from different authors. This variability caused confusion between scientists, among policy
makers and in the public. A methodical agreement generated by internationally recognized scientific
panels with expertise across a range of disciplines and clear science based orientation (e.g., [9,16,24])
seems to be urgently necessary.
Based on these, the objective of the present review is to characterize the most important influencing
factors along the food chain for calculation of CF for food of animal origin. The next section deals
with the whole food chain and its system boundaries followed by a critical assessment of the different
kinds of animal yields or specific outputs of animal production under special consideration of edible
protein and methods of their measurement/assessment.
2. Setting the Boundaries of a Production System and Further Influencing Factors Along the
Food Chain
2.1. Emissions Along the Food Chain
The IPCC [2] recommended GHG factors for CO2 (1), CH4 (23) and N2O (296) to calculate CF for
various processes. Recently there was some discussion about the factors and the IPCC [49] revised the
global warming potential of methane (CH4) from 23 to 25 because of indirect effects of CH4 on ozone
and stratospheric water vapour [9]. On the other hand, the Worldwatch Institute [50] suggests a Global
Warming Potential for CH4 of 72. Methane is a very important gas for CF calculation, especially for
food derived from ruminants. Between 50 and 80% of the total GHG emissions of food of ruminant
origin are due to methane [37,38].
The N2O-factor is given with around 300 (296 [2]; 298 [49]). From a global view the agricultural
N2O-emissions (from manure and soil; given in billion tonnes of CO2eq/y) are larger than calculated
methane emissions (2.5 versus 2.15 billion t CO2eq/y, [6]). Analogue tendencies are reported from
agriculture in the USA (222 million t CO2eq/y from N2O; 197 million t CO2eq/y from CH4; [51]). From
the view of science and policy, further research is required to considering a time horizon of the GHG
emissions [9,52].
In addition to GHG factors a possible exact measuring of climate relevant gases in all links along
the food chain is an essential prerequisite to calculate CF.
There is general agreement that carbon dioxide emissions from livestock metabolism are not
considered as a CO2-source in CF ([2,9], see Figure 1). CO2 has been fixed by photosynthesis in
phytogenic biomass and the C consumed in feed and emitted as CO2 by animals is considered as
equivalent or as emission neutral. On the other hand, CO2 from technical processes associated with
animal husbandry should be considered in CF calculations (for details see [7,10,11]).
Methane can be considered as an unavoidable by-product of anaerobic microbial fermentation,
especially in the rumen of ruminants, but also in the hindgut of all species and during anaerobic
manure management. Since energy losses via methane in the rumen are well known [53], animal
nutritionists have been trying to reduce the gastrointestinal methane emission from ruminants and in
the hindgut of further species for a long time. In 2005 around 90 million tonnes CH4 (about 1.9 billion t
CO2eq/y) were emitted from gastrointestinal fermentation of ruminants [6]. These emissions are
Animals 2012, 2
113
projected to grow by over 30% from 2000 to 2020 [6]. Enteric methane emissions (e.g., [54–57]),
methods of measurements (e.g., [58–61]) and reduction potentials (e.g., [62–65]) should not be further
considered here. Furthermore there are special issues of the journals “Animal Feed Science and
Technology” 145 (2008), pp. 209–419 and 166–167 (2011), pp. 1–782 and in the “Australian Journal
of Experimental Agriculture” 48, No. 1 and 2 (2008), dealing with the topics mentioned above.
Figure 1. Substantial elements of the chain to produce food of animal origin, as well as
selected inputs of resources and outputs of greenhouse gases (basic concept for system
boundaries [17]).
Inputs
Elements
Elements of
of
food
food chain
chain
Fertilizer,
Fuel,
Herbicids,
Seeds,
Water
Fuel,
Electricity
Fuel,
Electricity
Electricity,
Fuel
(CO2) 1)
Soil/
Plant
Feed,
Harvest,
Storage
Fuel,
Electricity
Food of animal
origin
Mixed feeds,
By-products
Men
Animals
Biogas,
Manure
Excrements
Outputs
of greenhouse
gases
CO2
N2O
CO2
CO2
CH4 (CO2) 1)
CH4
N2O
CO2
CH4
1)
CO2 will be fixed by photosynthesis and produced by animal metabolism, therefore it is
considered as emaissions-neutral.
Laughing gas (N20) has the highest GHG potential from the most relevant GHG [2]. It is not
directly excreted by animals; it depends on microbial conditions during manure management and in the
soil. Lower N-excretion by animals [66–68] and improved N-management (e.g., storing of manure,
adequate amounts of manure and fertilizer) may contribute to lower N-emissions from manure and soil
(e.g., [69–72]). More representative results from N2O measurements (also for grazing animals) may
substantially contribute to more reliable data for calculation of CF along the food chain. In some cases
specific emissions were excluded from calculations of CF due to data uncertainty (e.g., N2O from
leguminous pastures [37]). Such special situations should be mentioned in the study report to assess
the results.
2.2. Setting the System Boundaries
Definition of system boundaries along the food chain (see Figure 1 and [24]) is the starting point for
GHG measurements, for the calculation of CF of livestock products and for comparing results from
various studies [4,10]. There are some open questions which need to be answered and it should be
clearly defined whether they are or are not considered in the calculation, such as:
-
Consideration of emissions from land use and land use change [1]
Emissions from basic equipment (e.g., houses, machinery etc.; [38,73])
Transport, processing, trade of products of animal origin [38]
Emissions during preparing food from animal products in the kitchen/food processing
Use of an allocation of various animal products (see above)
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For example under Australian conditions Peters et al. [37] defined the system boundary in the case
of beef for all on-site and upstream processes at the farm, feedlot, and whole processing plant,
including transport between these sites.
Table 3 shows exemplary CF for milk under consideration of various boundaries. A clear definition
of the system boundaries and the comprehensibility are important prerequisites to follow the
calculations and to make the results comparable (e.g., [37,41,44]). Scientists working in this field
should come to agreements concerning system boundaries and GHG factors of climate relevant gases.
Table 3. Model calculation to demonstrate the effects of setting different boundaries for
CF of milk (g CO2eq per kg milk; 30 kg milk per day; diet on DM-base: 60% roughage,
40% concentrate; 4% milk fat, 3.4% protein; 305 days of lactation; 60 days dry period,
3 years lactation; 30 months calf and heifer period [38]).
System
1
2
3
4
5
6
7
System boundaries
Dairy cow emissions during lactation
1. + Emissions of feed production
2. + Dry period
3. + Heifer period
4. + Animal housing and milking
5. + Manure management
6. + Processing, transportation and trade of milk
CF (g CO2eq/kg milk)
280
430
500
730
760
820
1,100
3. Outcome of Animal Production
There is no essential need for food of animal origin for human beings, but the consumption of milk,
eggs, meat and fish may substantially contribute to a more balanced and palatable human diet.
Therefore one of the main goals of animal husbandry is the production of food of animal origin. Such
food contributes substantially to meeting the human requirements in essential amino acids (e.g., [74–76])
because of the high content in essential amino acids (such as lysine, methionine and cysteine,
threonine, leucine, etc.; see [77]). Furthermore, such food contains important minor nutrients like
major and trace minerals (such as Ca, P, Cu, Fe, I, Se, Zn) and vitamins (e.g., A, E, some B-vitamins,
especially B12) and has a considerable enjoyment value [78]. Human nutritionists [79,80] recommend
that about one third of the daily protein requirement (0.66–1 g per kg body weight and day; [75,80,81])
should originate from protein of animal origin to guarantee a more balanced diet, especially for “risk
groups” such as pregnant and lactating women, infants and children. Therefore, one endpoint, or the
outcome of specific animal yields could be edible protein or essential amino acids and should be
clearly defined. Otherwise there will be discrepancies in calculations and variations in the results
between various working groups as shown in Tables 1 and 2.
3.1. Milk and Eggs
Milk and eggs are clearly defined as food of animal origin. The yield can be measured as weight
(kg, etc.) or on the basis of standardized products (e.g., standardized protein, fat, dry matter or energy).
Therefore it is relatively easy to measure the animal yield for further calculations. But nevertheless,
there is a certain range between CF for milk (see Table 1).
Animals 2012, 2
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The composition of milk and eggs is well defined (see Table 6), but it may vary between various
sources and depending on animal breed, feeding and other influencing factors. Therefore the analysis
of milk and egg composition (protein; fat, lactose) may contribute to being more specific in measuring
the animal yield incl. the energy yield. Milk and eggs may be used entirely as food (except small
amounts of colostrum and egg shells; see Table 7).
3.2. Food from Slaughtered Animals
It is much more difficult to quantify and characterize the yield from the animal body after
slaughtering and processing. The GHG balance per kilogram body weight gain can only be calculated
on the farm level. Mialon et al. [82] carried out a feeding study with Blond d’Àquitaine bulls in the
finishing phase (400–650 kg body weight) including various feeding systems and weight gains
between 1,494 and 1,862 g/d and Doreau et al. [83] calculated a CF between 3.6 and 4.7 kg CO2eq
per kg body weight gain. Those values are similar to high daily weight gains as shown in Table 5, but
much lower than for lower weight gains. Normally, the GHG emissions for the whole beef system
include also emissions of cows, calves and heifers, needed to produce beef. They are much higher than
in the system dairy cow—growing/fattening bulls for beef (see allocation).
Mostly the term “meat” is used, but it is not clearly described, what it means (real meat or meat plus
bones). Peters et al. [37] introduced the term “hot standard carcass weight” (HSCW) as the weight at
the exit gate of the meat processing plant. It varies between 50–62% of the live weight of the cattle to
be slaughtered, but it may vary between 50% in the case of sheep and up to 80% for fattening turkeys
(e.g., [12,37,83]).
In the case of animals for meat/fish production the following endpoints can be measured:
-
Weight gain of the animal (per day or per growing period) during the whole life span
Weight gain of animal without gastro-intestinal tract
Empty body weight (or carcass weight; meat and bones; warm as HSCW or cold)
Meat (empty body minus bones)
Edible fraction (meat plus edible organs and tissues)
Edible protein (edible fractions of the carcass multiplied with their specific protein content).
Therefore it is really difficult to find an adequate CF for meat or edible products from slaughtered
animals. Various authors used different bases to calculate CF for products from slaughtered animals.
Williams et al. [12] estimated the killing out percentages for beef and poultry with 55 and 70% and 72,
75 and 77% for pigs with live weights of 76, 87 and 109 kg, respectively. Lesschen et al. [7] used
fixed values to calculate the carcass fraction from the final body weight of animals (e.g., 58% for beef;
75% for pork and 71% for poultry). Most authors used a fixed fraction of 0.9 for all animal species for
conversion of carcass weight to edible “meat”. De Vries and de Boer [5] used calculation factors to
determine the amount of edible product per kg live weight by 0.43; 0.53 and 0.56 for beef, pork and
poultry. Table 4 shows potential outputs for growing/fattening cattle under consideration of various
endpoints as mentioned above.
Calculation of CF may base on various outputs. For practical reasons carcass weight or weight gain
(warm or cold) would be the most important endpoint to measure the yield of slaughtered animals
Animals 2012, 2
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because this weight is measurable in the abattoir [37] and can be used for further calculations. Based
on the values derived from Table 4, CF is calculated for various endpoints under consideration of
differences in feeding and greenhouse gas emissions and is shown in Table 5.
Table 4. Model calculation to show various endpoints for growing/fattening bulls
(150–550 kg body weight; calculation based on data collected by [84]).
Gross
weight
gain
(g/day)
500
1,000
1,500
Weight gain
without content
of intestinal
tract (g/day)
438
900
1,385
Carcass
weight
(warm; % of
weight gain)
50
53
56
1
Carcass
weight gain
(warm;
g/day)
250
530
840
Meat gain
(% of
weight
gain)
40
44
48
Edible
fraction
gain 1
(g/day)
250
490
770
Meat
gain
(g/day)
200
440
720
Edible protein
(g/day; 19%
protein in
edible fraction)
48
93
146
Meat plus other edible tissues.
Table 5. Model calculations for CF of beef (150–550 kg body weight 1) depending on
feeding, weight gain, methane- and N2O-emissions and N-excretion [28]
Weight gain
(g/day)
Carbon footprints (kg CO2eq/kg)
Feed intake Portion
N2O-synthesis
Methane
Empty
N-excretion
(kg DM/ concentrate
Edible
emissions
(% of
Edible
Weight carcass
(g/day)
(% of DM(animal
fraction
(g/kg DM)
N-excretion) gain weight
Protein
x day)
intake) 1,2
gain
gain
500 (Pasture, no
6.5
concentrate)
1,000 (Indoor,
grass silage, some
7.0
concentrate)
1,500 (Indoor,
corn silage,
7.5
concentrate)
1
Production of calf up to 150
concentrate-DM.
0
26
110
2
11.5
23.0
28.0
110
15
24
130
1
5.5
11.0
13.8
55
30
22
150
0.5
3.5
7.0
9.0
35
kg BW is not considered; 2 CO2-Emission: 120 g/kg roughage-DM; 220 g/kg
3.3. Edible Protein as Most Important Objective of Animal Husbandry
The production of protein of animal origin is one of the most important goals of animal
husbandry [5]. On the other hand, the efficiency and the emissions of animal products can be also
compared on the basis of edible protein. The N or protein content of various foods of animal origin
may vary from values used for calculations in Table 6 (data by [84] on the basis of own studies).
Our data agrees with values used by Lesschen et al. [7], and it does not substantially disagree with
values from human food tables (see Table 6). De Vries and de Boer [5] used for their calculations
190 g protein/kg edible beef, pork and poultry meat; 30 g per kg milk products and 130 g per kg eggs.
Considering various influencing factors such as animal yields, feeding, edible fractions and protein
content in the edible fractions, the yield of edible protein per day and per kg body weight of animals is
given in Table 7.
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Table 6. Published data regarding the protein content of some edible animal products
(in g per kg edible product).
Product
[7]
Cows milk
Beef
Pork
Broiler
Eggs
References
[84]
1
[77]
[85]
33.3 (30.8–
32
34
34.4
37.0)
206
220 2 (206–227)
190
206–212
2
156
220 (195–240)
150
183–216
206
199
200
182–242
119
125
120
125
1
2
N-content × 6.25; Muscles only; n.d.: no data.
[86–89]
34
170–200
157 (129–178)
n.d.
121 (110-124)
The feeding may influence CF of food of animal origin. In the case of ruminants, higher amounts of
concentrate are required for higher animal yields. The proportion of by-products [90,91] used in
animal feeding does not only have nutritional implications, but it also affects the results of calculations
on land use [92]. There are large differences in protein yield per animal per day or per kg body weight
and day depending on animal species and category as well as their performances and the fractions
considered as edible (see Table 7).
Table 7. Influence of animal species, categories and performances on yield of edible
protein [84].
Edible
Dry matter
Roughage to
Protein in edible Edible Edible protein
Protein source Performance
fraction (%
intake (kg concentrate ratio
fraction (g per kg protein (g (g per kg body
(Body weight)
per day
of product or
per day) (on DM base, %)
fresh matter)
per day) weight and day)
body mass)
10 kg milk
20 kg milk
40 kg milk
Dairy goat
2 kg milk
5 kg milk
(60 kg)
500 g 1
Beef cattle
1,000 g 1
(350 kg)
1,500 g 1
500 g 1
Growing/fattening
700 g 1
pig (80 kg)
1,000 g 1
Broiler
40 g 1
60 g 1
(1.5 kg)
50% 2
Laying hen
70% 2
(1.8 kg)
90% 2
Dairy cow
(650 kg)
12
16
25
2
2.5
6.5
7.0
7.5
1.8
2
2.2
0.07
0.08
0.10
0.11
0.12
1
90/10
75/25
50/50
80/20
50/50
95/5
85/15
70/30
20/80
10/90
0/100
10/90
0/100
20/80
10/90
0/100
95
34
95
36
50
190
60
150
60
200
95
120
323
646
1292
68
170
48
95
143
45
63
81
4.8
7.2
3.4
4.8
6.2
0.5
1.0
2.0
1.1
2.8
0.14
0.27
0.41
0.56
0.8
1.0
3.2
4.8
1.9
2.7
3.4
Daily weight gain, 2 Laying performance.
Table 7 shows the highest protein yields per kg body weight for growing broilers as well as for
laying and lactating animals and the lowest values for growing/fattening ruminants. Based on those
values, emissions per kg edible protein are given in Table 8. Higher proportions of edible fractions or
Animals 2012, 2
118
higher protein content (e.g., 50 g protein per kg camel milk, [77]) as shown in Tables 6 and 7 may
increase the protein yield and reduce the CF per unit of product.
Apart from protein food of animal origin also contains fat and some carbohydrates which contribute
to human nutrition and which may replace energy of plant origin in human diets.
At high levels of performance there are remarkable differences in CO2 emissions due to human
consumption of 1 g protein from food of animal origin (eggs and meat from broiler < pork < milk <
beef, see Table 7). But here it has to be emphasized that this protein intake is accompanied—willingly
or not—by an energy intake from the protein itself, but also from further nutrients like lactose and fat
in milk or from fat in meat or eggs. Therefore, it should be avoided to attribute the CO2 burden to the
protein fraction (“edible protein”) exclusively. To prevent that this fact is neglected, there are different
alternatives:
In a first simple method, the CO2 emission due to 1 kg edible protein could be used as CO2 burden
of consumed energy (for example: 1 kg edible protein of eggs corresponds to about 8 kg egg
corresponding to 51.6 MJ energy (calculated by [77]); these combined intakes are related to 3 kg CO2).
One alternative could be a “nutritional allocation” (as described before for economic allocation),
meaning that the CO2 emissions are attributed to different functions of the food (source of
protein/source of energy/source of further essential nutrients).
Table 8. Influence of animal species, categories and performances on emissions (per kg
edible protein, own calculations).
Performance N-excretion
Methane
Emissions in kg per kg protein
per animal
(% of
emission
P
N
CH4 3
CO2eq
per day
intake)
(g per day) 3
10 kg milk
75
310
0.10
0.65
1.0
30
Dairy cow (650 kg) 20 kg milk
70
380
0.06
0.44
0.6
16
40 kg milk
65
520
0.04
0.24
0.4
12
2 kg milk
75
50
0.08
0.5
0.8
20
Dairy goat (60 kg)
5 kg milk
65
60
0.04
0.2
0.4
10
1
0.30
500 g
170
2.3
90
3.5
110
1
175
0.18
Beef cattle (350 kg) 1,000 g
84
1.3
1.7
55
1
180
80
0.14
1.0
1.2
1,500 g
35
16
0.12
1.0
0.20
5
85
500 g 1
Growing/fattening
12
0.08
0.7
0.12
5
80
700 g 1
pig (80 kg)
1
10
0.05
0.55
0.09
5
75
900 g
1
40 g
0.04
0.35
0.01
4
70
Broilers (1.5 kg)
Traces
0.03
0.25
0.01
3
60
60 g 1
2
7
50%
0.03
0.6
0.12
80
2
5
0.02
Laying hen (1.8 kg) 70%
0.4
Traces
0.07
65
2
3
0.02
0.3
0.05
55
90%
1
2
3
Daily weight gain Laying performance CH4-emission varies with composition of diet.
Protein source
(Body weight)
In a first simple step it is recommended to diminish the CO2 emission per 1 kg edible protein
(Table 8) by the CO2 amounts that would occur at an identical energy intake from food of plants
(energy from carbohydrates and fat). It means that an intake of 1 kg protein from eggs (corresponds to
Animals 2012, 2
119
8 kg eggs; see Table 7; and corresponding to 51.6 MJ energy) saves high amounts of other food (and
their CO2 burden). A more sophisticated way of an “allocation” within the foods could be to differentiate
between “protein derived energy” and “non-protein derived energy”. In milk and eggs more than 50%
of the total energy content is related to the non-protein-fraction (lactose/fat), therefore, it is questionable
whether the entire CO2 emission should be attributed only to the protein intake. Due to the very low
CO2 emission caused by energy intake of carbohydrates and fat from plants/seeds [12,15,17] it would
avoid/save high amounts of CO2 emissions, if the production of food of animal origin focussed on
“edible protein” and not on energy of non-proteinaceous fractions.
Furthermore animal products are not only used as food or respectively, as protein/amino acids, and
energy sources; they also offer some other important side-products such as skins or hides, fish meal or
meat and bone meal, etc. A kind of combined “nutritional/further purposes allocation” may contribute
to a more scientific assessment of CF for nutrient and energy supply as well as further uses.
Advantages and weaknesses of endpoints (outputs) of various types of animal production are
summarized in Table 9. All endpoints are characterized by some advantages and disadvantages. From
nutritional and scientific points of view the edible protein seems to be the most favourable
measurement, but its measurement is not easy and requires some analytical work (see Table 9). Land
requirements (e.g., arable land and/or grassland) as well types and intensities of food production may
be calculated on the basis of various protein sources for human nutrition. Such calculations can
contribute for better understanding of various conflicting aims in the field of food production, human
nutrition, use of unlimited and limited resources and resource efficiency, emissions and further points
in public discussion.
Table 9. Advantages and disadvantages of various outputs/endpoints of animal yields.
Animal yields
Milk, Eggs
Advantages
Easily measurable, almost complete
edible
Body weight gain
Easily measurable
Carcass weight
Easily measurable
Meat, edible fraction
Completely edible
Most important objective of animal
production; comparison of various
methods and sources to produce
protein of animal origin
Edible protein
Disadvantages
Variation in protein, fat and energy yield,
analyses may be useful
High portion of non edible fractions in the
gains
Contains still fractions which are not
edible (e.g., bones)
Categorization and separation not easy
Categorization of various fractions as
edible and difficulties to measure;
additional analytical work; variation in
N/protein content
4. Conclusions
Ranking of food of animal origin on the basis of CF may be indicative for some products, but may
also lead to wrong conclusions because of incompleteness of measuring animal yields and data bases,
system boundaries and other weaknesses. The data bases for GHG emissions should be improved and
the animal yields should be made comparable. Edible protein (or rather, essential amino acids and
some minor nutrients) of animal origin, being the most important objective of animal husbandry, is
Animals 2012, 2
120
proposed as a standard to compare various types and intensities of animal husbandry. Furthermore we
have to look at the whole food chain (see Figure 1) in order to decide whether a practice is sustainable
or not in the long term (e.g., [93,94]). In order to do this, however, further research is needed for more
reliable and resilient data.
Acknowledgments
The authors would like to thank to Manfred Grün for critical comments; Anne Mösseler for some
calculations; and Saara Sander and Sigrid Herweg for technical assistance.
Conflict of Interest
The authors declare no conflict of interest.
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